Fluorine-containing ion exchange membranes have excellent heat resistance, chemical resistance, and the like, and are used in various applications as electrolytic diaphragms for alkali chloride electrolysis, ozone producing electrolysis, fuel cells, water electrolysis, hydrochloric acid electrolysis, and the like.
Among these, in alkali chloride electrolysis where chlorine and alkali hydroxide are produced the ion exchange membrane process is primarily used in recent years. The ion exchange membrane used in the electrolysis of alkali chloride or the like is required to have various characteristics including, for example, maintaining operational characteristics of the ion exchange membrane in a favorable state for a long period of time, such as capability to maintain characteristics irrespective of a change in the catholyte concentration in a cathode chamber.
Patent Literature 1 discloses an ion exchange membrane consisting of at least two layers, i.e., a fluorine-containing polymer layer having a sulfonic acid group and a fluorine-containing polymer layer having a carboxylic acid group.